Radiation measurement



May 2, 1950 B. B. Rossi ETAL 2,506,435

RADIATION MEASUREMENT Fi1ed Ju1y 21, 1948 2 sheets-sheet 1 May 2, 1950 B. B. Rossl ET AL 2,505,435

RADIATION MEASUREMENT Filed Jqly 2l, 1948 2 Sl'xeets-Sheei'I 2 Patented May 2, 1950 areas f PA'rENr osmosi 2,506,435" RAnINrIoN MEAsmurineNr-y Bruno B-R`os's, Winchester-I; ,Massa Iarid-J ames SL Allem.. Champaign, .111., assignorsf to YthcfUnited` Statesof America'as represented by tlaeUnited States Atomic Energy Commission- Application J ixly '21, 1948,1 gerial No. 39,5878'l 3vv Glaims.- (CLfZ'BG-e-fm 'Ihis inventionirelates: tol an; improvement in methods and:I appar'a't'u'sf:V for: measuring thei intensity of radiations'and'nucleari' particles.`-

may `be transmittedovera. considerable' distance;

bythe' method: aI-idapparatus off tli'e` invention, radiation counters? may' be made" to" produce voltage pulsesoff anamplituue heretofore un'- known in-.suclif devices?.-

Geiierally the invention lies-inf pulsed operation of a radiationi'count'eriii-the voltage' region Where' a sparlcdischarge occurs. In the practice ofl` ther inventionsthe potential impressed between the electrodes of the counter is greater than the sparking potential of the electrode structureY and the gaseousionization medium' employed. Such operation relies uponthe' fact that l a potential-above the-sparking potential will not f produce a discharge until an ionizing particle enters the ionizing medium between the' electrodes. Thespark discharge which is' initiated by impingement of an ionizing particle results in a large voltage change across the counter. This large voltage surge may be registered without further amplification, even after transmission over a considerable length of transmission line. When the high voltage is withdrawn, the spark is quenched and the high voltage may again be impressed. No spark, and accordingly no voltage pulse, is produced if no ionizing event occurs within the radiation counter during the time that the interelectrode voltage is above the sparking potential. When such high voltages are impressed at spaced intervals, the number of voltage pulses produced by the radiation counter is proportional to the number of ionizing events occurring within the counter during the spaced intervals.

In accordance with the patent laws, the attached drawing illustrates a preferred embodiment of the invention, and the description below will serve to give a clearer understanding of the invention. In the drawing:

Fig; 1v isv a` schematic diagram, partially in lolock'-A form, of a system embodying'the-teachings'v of" thef invention;

Fig.v 2-'is fa' horizontal 'sectional View of a'c'ounter which may be' employed:- in practicing the in- Vention;

Fig. 3 is an Aend View v'infV elevationfofithe-counter ofFig. 2;'

Fig. 4' is'a vertical: sectionalcview takenv along the linelilz4 of Figa 2f'in.thedirection indicated by arrows; and.

Fig: Seis agraphirepresentationrof the-counting characteristics of theradiation counter of Fig; -21 when employed' in. the: systemy of. Fig. 1.

lfteferring'trst-l t'oFi-g.l 41f, afradiationf counter I 0 comprising-r a: cathode' lzzf'and" anianode I4' is connected in serieswithzsignal resistors It and I8,

whichareshunted'by condensers7 20 and 2-2, respectively, and with a sourceoif direct voltage M In.. seriesV Withthis'Y combination, which is similar t'o'f the'Y usual radiation. counter. circuit employedv with ani ordinary. GeigereMller counter; is al voltage?- source' resistor 2-6'. The voltage source resistor^2l isv coupled to'a square wave'pul'se generatorfzf'bya coupling condenser '303 The pulse generatori 2'8 producessquare wave pulses asI 'shown` at i 32; which pulsestare negative inpolarity?.` The voltage'souroe Zlhwhichv is in-` ser-ies with?` th'e voltage source' resistor" 26, impresseson thel'cathode IZ'avoltage` whichis'ne'ga'- tive with respect to" the anode f4; The pulses 325, which' arefsuper'imposedl on the direct voltage of theA source 24; increase" thet negative potential off' theic'ati'iode l2 with respectto the' anode M. voltage' source '241 i's' of a` Avalue below the extinction potentiaiioi'any ion dischargefbetween the cathode I2 and the anode I 4; preferably, however, the voltage source 24 is of sufficient magnitude to quickly collect the ions remaining in the counter il) after extinction of a discharge by termination of a pulse 32. The pulses 32 are of sufficient amplitude, when added to the voltage of the source 24, to bring the voltage across the counter l0 above the sparking potential. The sparking potential is a potential of such value that discharge in the counter is of avalanche type, that is, the discharge occurs in the gas tube characteristic continuous discharge region. Thus any ionizing event such as the emission of an electron from the cathode by impingement of a gamma ray during a pulse 32 produces a spark discharge across the counter It which produces a large voltage pulse 36, of the order of 50 Volts or more, across the signal resistor I8. These pulses 36 are of sufficient amplitude to trigger a conventional one shot multivibrator 38 without the insertion of additional amplication, even where a long transmission line (not shown) is inserted in the circuit. The output pulses of the multivibrator 3B are recorded on a message register 40 in conventional fashion.

In Figs. 2, 3 and 4 is illustrated a simply constructed radiation counter which may be employed as the counter I of Fig. 1. The cathode I2 is a platinum tube of 0.125 inside diameter and 0.005" thickness. The anode I4 is a 0.005" tungsten wire. The cathode I2 rests in apertures 50 in insulating support bars 52, of methyl methacrylate polymer. The apertures 50 in the support bars 52 have outer portions 54 of slightly enlarged diameter to form shoulders 56. Resting against the shoulders 56 are methyl methacrylate end caps 53 and E5. The end caps 58 and 60 are axially apertured at 52 and 64, respectively, and the anode I4 extends through these apertures. At one end, the anode wire I4 is soldered to the end 56 of a compressed coiled spring 68, which rests in a cup-shaped cavity 'I0 in the outer end of the end cap 53. At the other end the anode wire I is spot welded at 'I2 to a rectangular plate 'I4 of stainless steel which is retained in place by longitudinal slots 'I6 in the outer end of the end cap t0. The end caps 58 and 60 have wall apertures 'I3 therein to permit free flow of gas between the interior of the counter and the surrounding atrnosphere, which is preferably an inert gas such as argon at a pressure somewhat near atmospheric pressure. A large number of such counters may be mounted in a single assembly within a single gas-tight enclosure (not illustrated) By providing a common gaseous atmosphere, the counters are made to demonstrate similar characteristics.

In Fig. 5 are shown the characteristics of the counter illustrated in Fig. 2 when employed in a circuit such as shown in Fig. 1. In the particular circuit employed, the pulse generator 28 provided a square wave 32 of 450 volts amplitude and 150 microseconds duration, with a repetition rate of 6 per second. The counter gas was argon at 59 centimeters Hg. A gamma ray source was placed near the counter tube. Fig. 5, which is similar in appearance to the plateau curve of a conventional Geiger-Mller counter, shows the number of counts per minute registered as a function of the direct voltage of the voltage source 24, designated Base voltage in the drawing. It will be seen from Fig. 5 that there is a plateau oi' approximately 200 volts over which the counting rate is substantially constant.

It will be understood that the embodiment of the invention described above is merely illustrative. Persons skilled in the art will readily adapt the teachings of the invention to a large variety of equivalent devices.

What is claimed is:

1. In radiation measurement apparatus, in combination: a radiation counter having an anode, a cathode and an ionizing medium between said electrodes; and a source of direct voltage having superimposed thereon voltage pulses of alternately positive and negative phase coupled to said electrodes, the voltage pulses having an amplitude sufficient to alternately impress on said electrodes a voltage above the sparking potential and a voltage below the extinction potential thereof.

2. In radiation measurement apparatus, in combination: a radiation counter having an anode, a cathode and an ionizing medium between said electrodes; a source of direct voltage and serially coupled thereto a source of voltage pulses of alternately positive and negative phase coupled to said electrodes, the voltage pulses of positive phase having an amplitude suilicient to .impress on said electrodes a voltage above the sparking potential and the pulses of negative phase causing the impression thereon of a Voltage below the extinction potential thereof, and means coupled to the counter for registering the ionization pulses occurring therein.

3. In radiation measurement apparatus, in combination: a radiation counter having an anode, a cathode and an ionizing m'edium between said electrodes; a source of direct voltage impressed upon said electrodes; and a source of alternately positive and negative voltage pulses coupled to said electrodes and superimposed upon said direct voltage, the sum of the voltage pulses and the direct voltage having a magnitude to alternately impress on said electrodes a voltage above the sparking potential and a voltage below the extinction potential thereof.

BRUNO B. ROSSI. JAMES S. ALLEN.

REFERENCES CITED The following references are of record in the file of this patent:

'UNITED STATES PATENTS Number Name Date 2,418,892 Lord I Apr. l5, 1947 

